The present invention is a system for providing GPS users with a high level of confidence in the integrity and accuracy of received GPS signals. The system provides a means for each GPS satellite itself to verify the accuracy and/or integrity of its own operations by calculations and processing internal to the GPS satellite and by crosslink communications with other GPS satellites in the GPS constellation. After a GPS satellite verifies the accuracy and/or integrity of its own signals, the GPS satellite transmits an integrity message to all GPS users in view of the satellite. The integrity message can alert GPS users to a loss of integrity or accuracy in the GPS signals. Alternatively, the integrity message can contain information to correct errors in the GPS signals. The integrity message can be incorporated into the existing GPS navigation message transmitted by GPS satellites, or the integrity message can be transmitted over a separate channel such as the planned L5 band channel.
GPS receivers will receive and decode the integrity messages transmitted by individual GPS satellites. The GPS receivers will then be able to determine whether or not the GPS signals being received have integrity. If the integrity message contains correction data, the GPS receivers can use the correction data to correct the GPS signals. The GPS users will thus be provided with very high confidence in the integrity, accuracy, and reliability of the GPS position and time data. This confidence will enable many new applications to be adopted by the civil community and general public.
Because the system of the present invention allows the GPS satellites themselves to verify their own integrity and/or accuracy, the system eliminates the enormous cost and complexity associated with proposed ground-based GPS integrity monitoring systems like the WAAS. The system of the present invention also provides faster response times and more robust operation than proposed ground based monitoring systems. Additionally, because the GPS satellites themselves report their integrity to GPS users, the need for an independent messaging system is eliminated. As an option, the system could be used in conjunction with a ground-based monitoring system like WAAS, to provide the highest degree of integrity and the lowest probability of GPS error.
The satellite-based GPS monitoring system described herein has three separate component systems:
1. GPS Automated Satellite Signal Waveform Monitor
2. GPS Automated Satellite Position Monitor System
3. GPS Beacon for Auto-registration with Earth Coordinates
The Satellite Signal Waveform monitor system allows the GPS satellite to receive its own transmissions and check the integrity of its own transmissions. The Satellite Position Monitor system provides the GPS satellite the capability to send its transmissions to one or more other GPS satellites which then verify the integrity of the transmissions from the originating GPS satellite and send back an integrity message indicating the integrity of the transmissions. The GPS Beacon allows the GPS satellite to verify its operation by receiving a signal from a beacon at a fixed known location. By receiving beacon position data from other GPS satellites, the GPS satellite can compare the beacon position data with satellite position data stored in the GPS satellite. If the data correlates within a certain error, the GPS satellite can determine whether it is operating properly.
Any or all of the above systems and methods can be used to allow GPS satellites to verify their own integrity and/or accuracy of their transmissions. The GPS users will thus be provided with very high confidence in the integrity, accuracy, and reliability of the GPS position and time data. This confidence will enable many new applications to be adopted by the civil community and general public.